Air conditioner and method for controlling operation of air conditioner

ABSTRACT

An air conditioner includes a compressor having a compressor motor including coils, an indoor fan having a fan motor, a connection switching unit that switches a connection state of the coils between a first connection state and a second connection state in which a line voltage is lower than a line voltage in the first connection state, and a controller that controls the compressor motor, the fan motor, and the connection switching unit. The controller provides a stop period during which rotation of the compressor motor stops before the connection switching unit switches the connection state of the coils, and rotates the fan motor for at least a time period within the stop period.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of InternationalPatent Application No. PCT/JP2017/017650 filed on May 10, 2017, thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an air conditioner and a method forcontrolling an operation of the air conditioner.

BACKGROUND

In an air conditioner, a connection state of coils in a compressor motoris switched between a Y connection (star connection) and a deltaconnection (also referred to as A connection) in order to enhanceoperation efficiency of a compressor when the compressor rotates at alow speed and when the compressor rotates at a high speed.

Switching of the connection states of the coils is performed in a statewhere the compressor motor stops, in consideration of reliability or thelike of a device (see, for example, Patent Reference 1).

PATENT REFERENCE

Patent Reference 1: Japanese Patent Application Publication No.2009-216324 (see paragraphs 0027-0039).

However, since the compressor motor stops when the connection state ofthe coils is switched, an operation of the air conditioner istemporarily stopped, and thus user comfort may be reduced.

SUMMARY

The present invention is intended to solve the above described problem,and an object of the present invention is to provide an air conditionerand a method for controlling an operation of the air conditioner capableof suppressing reduction in comfort.

An air conditioner of the present invention includes a compressor havinga compressor motor having coils, an indoor fan having a fan motor, aconnection switching unit to switch a connection state of the coilsbetween a first connection state and a second connection state in whicha line voltage is lower than a line voltage in the first connectionstate, and a controller to control the compressor motor, the fan motor,and the connection switching unit. The controller provides a stop periodduring which rotation of the compressor motor stops before theconnection switching unit switches the connection state of the coils,and causes the fan motor to rotate for at least a time period within thestop period.

According to the present invention, the fan motor rotates for at least atime period within the stop period during which driving of thecompressor motor is stopped. Thus, reduction in comfort can besuppressed by air blowing by the fan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of an air conditionerof a first embodiment.

FIG. 2 is a conceptual diagram showing a basic configuration of acontroller in the air conditioner of the first embodiment.

FIG. 3(A) is a block diagram showing a control system of the airconditioner of the first embodiment, and FIG. 3(B) is a block diagramshowing a part of the control system that controls a compressor motorbased on an indoor temperature.

FIG. 4 is a sectional view showing a compressor of the first embodiment.

FIG. 5 is a sectional view showing the compressor motor of the firstembodiment.

FIG. 6 is a block diagram showing a driving device that drives thecompressor motor of the first embodiment.

FIG. 7 is a block diagram showing the driving device that drives thecompressor motor of the first embodiment.

FIGS. 8(A) and 8(B) are schematic diagrams showing a switching operationof a connection state of the coils in the first embodiment.

FIG. 9 is a schematic diagram showing the connection state of the coilsin the first embodiment.

FIG. 10 is a flowchart for explaining a method for controlling anoperation of the air conditioner of the first embodiment.

FIG. 11 is a flowchart for explaining the operation control method ofthe air conditioner of the first embodiment.

FIG. 12 is a block diagram showing another configuration example of thedriving device in the first embodiment.

FIG. 13 is a flowchart for explaining a method for controlling anoperation of an air conditioner of a second embodiment.

FIG. 14 is a flowchart for explaining a method for controlling anoperation of an air conditioner of a third embodiment.

FIG. 15 is a flowchart for explaining a method for controlling anoperation of an air conditioner of a fourth embodiment.

FIGS. 16(A) and 16(B) are schematic diagrams showing a switchingoperation of a connection state in an air conditioner of a fifthembodiment.

FIGS. 17(A) and 17(B) are schematic diagrams showing another example ofthe switching operation of the connection state in the air conditionerof the fifth embodiment.

DETAILED DESCRIPTION First Embodiment

(Configuration of Air Conditioner)

First, an air conditioner 5 of a first embodiment of the presentinvention will be described. FIG. 1 is a block diagram showing aconfiguration of the air conditioner 5. The air conditioner 5 includesan indoor unit 5A installed in a room (space to be air-conditioned) andan outdoor unit 5B installed outside the room. The indoor unit 5A andthe outdoor unit 5B are connected by connection pipes 40 a and 40 bthrough which refrigerant flows. Liquid refrigerant passing through acondenser flows through the connection pipe 40 a. Gas refrigerantpassing through an evaporator flows through the connection pipe 40 b.

The outdoor unit 5B is provided with a compressor 8 that compresses anddischarges refrigerant, a four-way valve (refrigerant flow pathswitching valve) 42 that switches a flow direction of the refrigerant,an outdoor heat exchanger 43 that exchanges heat between outside air andthe refrigerant, and an expansion valve (decompressor) 44 that reducespressure of the high-pressure refrigerant to a low pressure. Thecompressor 8 is constituted by, for example, a rotary compressor shownin FIG. 4. In the indoor unit 5A, an indoor heat exchanger 45 thatperforms heat exchange between indoor air and the refrigerant isdisposed.

The compressor 8, the four-way valve 42, the outdoor heat exchanger 43,the expansion valve 44, and the indoor heat exchanger 45 are connectedby a pipe 40 including the above described connection pipes 40 a and 40b, and constitute a refrigerant circuit. These components constitute acompression refrigeration cycle (compression heat pump cycle) in whichthe refrigerant circulates.

In order to control an operation of the air conditioner 5, an indoorcontroller 50 a is disposed in the indoor unit 5A, and an outdoorcontroller 50 b is disposed in the outdoor unit 5B. Each of the indoorcontroller 50 a and the outdoor controller 50 b has a control board onwhich various circuits for controlling the air conditioner 5 are formed.The indoor controller 50 a and the outdoor controller 50 b are connectedto each other by a communication cable 50 c. The communication cable 50c is bundled together with the above described connection pipes 40 a and40 b, for example.

In the outdoor unit 5B, an outdoor fan 6 which is a blower is disposedto face the outdoor heat exchanger 43. The outdoor fan 6 includes animpeller 62 and an outdoor fan motor 61 that rotates the impeller 62.The impeller 62 is constituted by, for example, a propeller fan. By airblowing by the outdoor fan 6, an air flow passing through the outdoorheat exchanger 43 is generated.

The four-way valve 42 is controlled by the outdoor controller 50 b, andswitches the flow direction of the refrigerant. When the four-way valve42 is in a position indicated by a solid line in FIG. 1, gas refrigerantdischarged from the compressor 8 is sent to the outdoor heat exchanger43 (condenser). When the four-way valve 42 is in a position indicated bya broken line in FIG. 1, gas refrigerant flowing from the outdoor heatexchanger 43 (evaporator) is sent to the compressor 8. The expansionvalve 44 is controlled by the outdoor controller 50 b, and changes itsopening degree to reduce the pressure of the high pressure refrigerantto a low pressure.

In the indoor unit 5A, an indoor fan 7 which is a blower is disposed toface the indoor heat exchanger 45. The indoor fan 7 includes an impeller72 and an indoor fan motor 71 (fan motor) that rotates the impeller 72.The impeller 72 is constituted by, for example, a crossflow fan. By airblowing by the indoor fan 7, an air flow passing through the indoor heatexchanger 45 is generated, and air (conditioned air) subjected to heatexchange in the indoor heat exchanger 45 is supplied to the room.

The indoor unit 5A is provided with an indoor temperature sensor 54 as atemperature sensor. The indoor temperature sensor 54 measures an indoortemperature Ta that is a temperature of indoor air, and transmits themeasured temperature information (information signal) to the indoorcontroller 50 a. The indoor temperature sensor 54 may be constituted bya temperature sensor which is used in a general air conditioner.Alternatively, a radiant temperature sensor that detects a surfacetemperature of a wall, a floor, or the like in the room may be used.

The indoor unit 5A is further provided with a signal receiver 56. Thesignal receiver 56 receives an instruction signal (operation instructionsignal) transmitted from a remote controller 55 as an operation deviceoperated by a user. The remote controller 55 is used by the user to givethe air conditioner 5 instructions of operation inputs (start and stopof operation), operation modes (cooling, heating, or the like), andoperation content (set temperature, wind speed, or the like). The remotecontroller 55 corresponds to a temperature setting part for setting anindoor temperature Ta (set temperature). In this regard, setting of theindoor temperature Ta is not limited to setting by the remote controller55, and the indoor temperature Ta may be set by the indoor controller 50a based on the operation mode, the operation content, or the like.

The compressor 8 has a compressor motor 1 (FIG. 5). The compressor 8 isconfigured to be capable of changing a rotation speed in a range of 20to 130 rps during a normal operation. An amount of refrigerantcirculating in the refrigerant circuit increases, as the rotation speedof the compressor 8 increases. The rotation speed of the compressor 8 iscontrolled by a controller 50 (more specifically, the outdoor controller50 b) according to a temperature difference ΔT between the indoortemperature Ta detected by the indoor temperature sensor 54 and a settemperature Ts set by the user with the remote controller 55. As thetemperature difference ΔT increases, the compressor 8 rotates at ahigher rotation speed, and thus the circulating amount of therefrigerant increases.

Rotation of the indoor fan 7 is controlled by the indoor controller 50a. The rotation speed of the indoor fan 7 is switchable to a pluralityof stages. In this example, the rotation speed of the indoor fan 7 canbe switched, for example, to three stages, that is, strong wind,intermediate wind, and weak wind. When the wind speed is set to anautomatic mode by the remote controller 55, the rotation speed of theindoor fan 7 is switched in accordance with the temperature differenceΔT between the measured indoor temperature Ta and the set temperatureTs.

Rotation of the outdoor fan 6 is controlled by the outdoor controller 50b. The rotation speed of the outdoor fan 6 is switchable to a pluralityof stages. In this example, the rotation speed of the outdoor fan 6 isswitched in accordance with the temperature difference ΔT between themeasured indoor temperature Ta and the set temperature Ts.

The indoor unit 5A includes a lateral wind direction plate 48 and avertical wind direction plate 49. The lateral wind direction plate 48and the vertical wind direction plate 49 change a blowing direction inwhich the conditioned air subjected to heat exchange in the indoor heatexchanger 45 is blown into the room by the indoor fan 7. The lateralwind direction plate 48 changes the blowing direction laterally, whereasthe vertical wind direction plate 49 changes the blowing directionvertically. An angle of each of the lateral wind direction plate 48 andthe vertical wind direction plate 49, that is, a direction of the blownairflow is controlled by the indoor controller 50 a based on the settingby the remote controller 55.

A basic operation of the air conditioner 5 is as follows. During acooling operation, the four-way valve 42 is switched to the positionindicated by the solid line, and high-temperature and high-pressure gasrefrigerant discharged from the compressor 8 flows into the outdoor heatexchanger 43. In this case, the outdoor heat exchanger 43 operates as acondenser. When air passes through the outdoor heat exchanger 43 by therotation of the outdoor fan 6, the air absorbs heat of condensation fromthe refrigerant via heat exchange. The refrigerant is condensed into thehigh-pressure and low-temperature liquid refrigerant, and isadiabatically expanded in the expansion valve 44 to become low-pressureand low-temperature two-phase refrigerant.

The refrigerant passing through the expansion valve 44 flows into theindoor heat exchanger 45 of the indoor unit 5A. The indoor heatexchanger 45 operates as an evaporator. When air passes through theindoor heat exchanger 45 by the rotation of the indoor fan 7, heat ofevaporation is taken from the air by the refrigerant via heat exchange.Thus, the cooled air is supplied to the room. The refrigerant evaporatesto become low-temperature and low-pressure gas refrigerant, and iscompressed by the compressor 8 to become high-temperature andhigh-pressure refrigerant again.

During a heating operation, the four-way valve 42 is switched to aposition indicated by the dotted line, and the high-temperature andhigh-pressure gas refrigerant discharged from the compressor 8 flowsinto the indoor heat exchanger 45. In this case, the indoor heatexchanger 45 operates as a condenser. When air passes through the indoorheat exchanger 45 by the rotation of the indoor fan 7, the air absorbsheat of condensation from the refrigerant via heat exchange. Thus, theheated air is supplied to the room. The refrigerant is condensed intothe high-pressure and low-temperature liquid refrigerant, and isadiabatically expanded in the expansion valve 44 to become low-pressureand low-temperature two-phase refrigerant.

The refrigerant passing through the expansion valve 44 flows into theoutdoor heat exchanger 43 of the outdoor unit 5B. The outdoor heatexchanger 43 operates as an evaporator. When air passes through theoutdoor heat exchanger 43 by the rotation of the outdoor fan 6, heat ofevaporation is taken from the air by the refrigerant via heat exchange.The refrigerant evaporates to become low-temperature and low-pressuregas refrigerant, and is compressed by the compressor 8 to becomehigh-temperature and high-pressure refrigerant.

FIG. 2 is a conceptual diagram showing a basic configuration of acontrol system of the air conditioner 5. The above described indoorcontroller 50 a and outdoor controller 50 b exchange informationtherebetween via the communication cable 50 c to control the airconditioner 5. In this example, a combination of the indoor controller50 a and the outdoor controller 50 b will be referred to as thecontroller 50.

FIG. 3(A) is a block diagram showing the control system of the airconditioner 5. The controller 50 is constituted by, for example, amicrocomputer. The controller 50 incorporates an input circuit 51, anarithmetic circuit 52, and an output circuit 53.

An instruction signal received by the signal receiver 56 from the remotecontroller 55 is input to the input circuit 51. The instruction signalincludes, for example, signals for setting an operation input, anoperation mode, a set temperature, an air volume, and a wind direction.Temperature information indicating the indoor temperature Ta detected bythe indoor temperature sensor 54 is also input to the input circuit 51.The input circuit 51 outputs these input information to the arithmeticcircuit 52.

The arithmetic circuit 52 includes a central processing unit (CPU) 57and a memory 58. The CPU 57 performs arithmetic processing anddetermination processing. The memory 58 stores various setting valuesand programs used for controlling the air conditioner 5. The arithmeticcircuit 52 performs arithmetic and determination based on theinformation input from the input circuit 51, and outputs the result tothe output circuit 53.

The output circuit 53 outputs control signals to the compressor motor 1,a connection switching unit 15, a converter 102, an inverter 103, thefour-way valve 42, the expansion valve 44, the outdoor fan motor 61, theindoor fan motor 71, the lateral wind direction plate 48, and thevertical wind direction plate 49, based on the information input fromthe arithmetic circuit 52.

As described above, the indoor controller 50 a and the outdoorcontroller 50 b (FIG. 2) exchange information with each other via thecommunication cable 50 c to control various devices of the indoor unit5A and the outdoor unit 5B. Thus, a combination of the indoor controller50 a and the outdoor controller 50 b is referred to as the controller50. In practice, each of the indoor controller 50 a and the outdoorcontroller 50 b is constituted by, for example, a microcomputer. In thisregard, only one of the indoor unit 5A and the outdoor unit 5B may beprovided with the controller to control various devices in the indoorunit 5A and the outdoor unit 5B.

FIG. 3(B) is a block diagram showing a part of the controller 50 thatcontrols the compressor motor 1 based on the indoor temperature Ta. Thearithmetic circuit 52 of the controller 50 includes a received contentanalysis unit 52 a, an indoor temperature acquiring unit 52 b, atemperature difference calculation unit 52 c, and a compressorcontroller 52 d. These units are included in, for example, the CPU 57 ofthe arithmetic circuit 52.

The received content analysis unit 52 a analyzes an instruction signalinput from the remote controller 55 via the signal receiver 56 and theinput circuit 51. The received content analysis unit 52 a outputs, forexample, the operation mode and the set temperature Ts based on theanalysis result to the temperature difference calculation unit 52 c. Theindoor temperature acquiring unit 52 b acquires the indoor temperatureTa input from the indoor temperature sensor 54 via the input circuit andoutputs the acquired indoor temperature Ta to the temperature differencecalculation unit 52 c.

The temperature difference calculation unit 52 c calculates atemperature difference ΔT between the indoor temperature Ta input fromthe indoor temperature acquiring unit 52 b and the set temperature Tsinput from the received content analysis unit 52 a. When the operationmode input from the received content analysis unit 52 a is the heatingoperation, the temperature difference ΔT is calculated as ΔT=Ts−Ta. Whenthe operation mode is the cooling operation, the temperature differenceΔT is calculated as ΔT=Ta−Ts. The temperature difference calculationunit 52 c outputs the calculated temperature difference ΔT to thecompressor controller 52 d.

The compressor controller 52 d controls a driving device 100 based onthe temperature difference ΔT input from the temperature differencecalculation unit 52 c, thereby controlling the rotation speed of thecompressor motor 1 (i.e., the rotation speed of the compressor 8).

(Configuration of Compressor)

Next, a configuration of the compressor 8 will be described. FIG. 4 is across-sectional view showing a configuration of the compressor 8. Thecompressor 8 is constituted as, for example, a rotary compressor, andincludes a shell 80, a compression mechanism 9 disposed in the shell 80,and the compressor motor 1 that drives the compression mechanism 9. Thecompressor 8 further includes a shaft 90 (crankshaft) that connects thecompressor motor 1 and the compression mechanism 9 to each other so thata driving force can be transmitted between the compressor motor 1 andthe compression mechanism 9. The shaft 90 is fitted into a shaft hole 27(FIG. 5) of the rotor 20 of the compressor motor 1.

The shell 80 is a closed container formed of, for example, a steelsheet, and covers the compressor motor 1 and the compression mechanism9. The shell 80 has an upper shell 80 a and a lower shell 80 b. Theupper shell 80 a is provided with a glass terminal 81 as a terminal partfor supplying electric power from the outside of the compressor 8 to thecompressor motor 1, and a discharge pipe 85 for discharging therefrigerant compressed in the compressor 8 to the outside. In thisexample, six lead wires in total are drawn out of the glass terminal 81,and the six lead wires include two lead wires for each of U-phase,V-phase, and W-phase of the coils 3 of the compressor motor 1 (FIG. 5).The lower shell 80 b houses the compressor motor 1 and the compressionmechanism 9.

The compression mechanism 9 has an annular first cylinder 91 and anannular second cylinder 92 along the shaft 90. The first cylinder 91 andthe second cylinder 92 are fixed to an inner peripheral part of theshell 80 (lower shell 80 b). An annular first piston 93 is disposed onan inner peripheral side of the first cylinder 91, and an annular secondpiston 94 is disposed on an inner peripheral side of the second cylinder92. The first piston 93 and the second piston 94 are rotary pistons thatrotate together with the shaft 90.

A partition plate 97 is provided between the first cylinder 91 and thesecond cylinder 92. The partition plate 97 is a disk-shaped memberhaving a through hole at its center. A cylinder chamber of each of thefirst cylinder 91 and the second cylinder 92 is provided with a vane(not shown) that separates the cylinder chamber into a suction side anda compression side. The first cylinder 91, the second cylinder 92, andthe partition plate 97 are integrally fixed together by bolts 98.

An upper frame 95 is disposed on an upper side of the first cylinder 91to cover an upper side of the cylinder chamber of the first cylinder 91.A lower frame 96 is disposed on a lower side of the second cylinder 92to cover a lower side of the cylinder chamber of the second cylinder 92.The upper frame 95 and the lower frame 96 rotatably support the shaft90.

Refrigerating machine oil (not shown) for lubricating sliding parts ofthe compression mechanism 9 is stored in a bottom part of the lowershell 80 b of the shell 80. The refrigerating machine oil flows upwardthrough a hole 90 a formed in the axial direction in the shaft 90, andis supplied to the sliding parts from oil supply holes 90 b formed at aplurality of positions of the shaft 90.

A stator 10 of the compressor motor 1 is fitted to an inner side of theshell 80 by shrink fitting. Electric power is supplied to the coils 3 ofthe stator 10 from the glass terminal 81 attached to the upper shell 80a. The shaft 90 is fixed to the shaft hole 27 (FIG. 5) of the rotor 20.

An accumulator 87 for storing refrigerant gas is attached to the shell80. The accumulator 87 is held by, for example, a holding part 80 cprovided on an outer side of the lower shell 80 b. A pair of suctionpipes 88 and 89 are attached to the shell 80, and the refrigerant gas issupplied from the accumulator 87 to the cylinders 91 and 92 via thesuction pipes 88 and 89.

For example, R410A, R407C, R22, or the like may be used as therefrigerant. A low GWP (global warming coefficient) refrigerant isdesirably used from the viewpoint of preventing global warming. Forexample, the following refrigerant may be used as the low GWPrefrigerant.

(1) First, a halogenated hydrocarbon having a carbon double bond in itscomposition, such as hydro-fluoro-olefin (HFO)-1234yf (CF₃CF=CH₂), canbe used. The GWP of HFO-1234yf is 4.

(2) A hydrocarbon having a carbon double bond in its composition, suchas R1270 (propylene), may also be used. The GWP of R1270 is 3, which islower than that of HFO-1234yf, but flammability of R1270 is higher thanthat of HFO-1234yf.

(3) A mixture containing at least one of a halogenated hydrocarbonhaving a carbon double bond in its composition or a hydrocarbon having acarbon double bond in its composition, such as a mixture of HFO-1234yfand R32, may also be used. The above described HFO-1234yf islow-pressure refrigerant and tends to cause large pressure loss, and maycause degradation of performance of a refrigeration cycle (especially,an evaporator). For this reason, a mixture of HFO-1234yf and either R32or R41 which is higher pressure refrigerant than HFO-1234yf is desirablein practice.

A basic operation of the compressor 8 is as follows. Refrigerant gassupplied from the accumulator 87 is supplied to the cylinder chambers ofthe first cylinder 91 and the second cylinder 92 through the suctionpipes 88 and 89. When the compressor motor 1 is driven to rotate therotor 20, the shaft 90 rotates together with the rotor 20. Then, thefirst piston 93 and the second piston 94 fitted to the shaft 90 rotateeccentrically in the cylinder chambers to compress the refrigerant inthe cylinder chambers. The compressed refrigerant flows upward in theshell 80 through holes (not shown) provided in the rotor 20 of thecompressor motor 1 and is then discharged to the outside through thedischarge pipe 85.

(Configuration of Compressor Motor)

Next, a configuration of the compressor motor 1 will be described. FIG.5 is a sectional view showing a configuration of the compressor motor 1of the first embodiment. The compressor motor 1 is a permanent magnetembedded motor. The compressor motor 1 includes a stator 10 and a rotor20 rotatably provided inside the stator 10. An air gap of, for example,0.3 to 1 mm, is formed between the stator 10 and the rotor 20. FIG. 5 isa cross-sectional view taken along a plane perpendicular to a rotationaxis of the rotor 20.

Hereinafter, an axial direction (a direction of the rotation axis) ofthe rotor 20 will be simply referred to as an “axial direction”. Adirection along an outer periphery (circumference) of each of the stator10 and the rotor 20 will be simply referred to as a “circumferentialdirection”. A radial direction of each of the stator 10 and the rotor 20is simply referred to as a “radial direction”.

The stator 10 includes a stator core 11 and coils 3 wound around thestator core 11. The stator core 11 is obtained by stacking a pluralityof electromagnetic steel sheets each having a thickness of 0.1 to 0.7 mm(here, 0.35 mm) in the direction of the rotation axis and fixing thesteel sheets by crimping.

The stator core 11 includes an annular yoke part 13 and a plurality oftooth parts 12 (in this example, nine tooth parts) protruding inward inthe radial direction from the yoke part 13. A slot is formed betweeneach adjacent two tooth parts 12. Each of the tooth parts 12 has a toothend part at an end on an inner side in the radial direction, and thetooth end part has a wider width (a dimension in the circumferentialdirection of the stator core 11).

The coil 3 as a stator winding is wound around each of the tooth parts12 via an insulating body (insulator) 14. The coil 3 is obtained by, forexample, winding a magnet wire having a wire diameter (diameter) of 0.8mm around each of the tooth parts 12 by concentration winding in 110turns. The number of turns and the wire diameter of each coil 3 aredetermined in accordance with properties (rotation speed, torque, or thelike) required for the compressor motor 1, a supply voltage, or across-sectional area of the slot.

The coils 3 are constituted by three-phase windings of a U-phase, aV-phase and a W-phase (referred to as coils 3U, 3V and 3W). Bothterminals of the coil 3 of each phase are opened. That is, the coils 3have six terminals in total. A connection state of the coils 3 isswitchable between a Y connection and a delta connection, which will bedescribed later. The insulator 14 is made of, for example, a film formedof polyethylene terephthalate (PET) and has a thickness of 0.1 to 0.2mm.

The stator core 11 has a configuration in which a plurality of (nine inthis example) blocks are connected together via thin-wall parts. Themagnet wire is wound around each of the tooth parts 12 in a state wherethe stator core 11 is unfolded in a belt shape, and then the stator core11 is bent in a ring shape and both ends of the stator core are weldedto each other. The stator core 11 is not limited to the above describedconfiguration in which the plurality of blocks (divided cores) areconnected together.

The rotor 20 includes a rotor core 21 and permanent magnets 25 attachedto the rotor core 21. The rotor core 21 is obtained by stacking aplurality of electromagnetic steel sheets each having a thickness of 0.1to 0.7 mm (0.35 mm in this example) in the direction of the rotationaxis and fixing the steel sheets by crimping.

The rotor core 21 has a cylindrical shape and has the shaft hole 27(center hole) formed at a center in the radial direction. The shaft asthe rotation axis of the rotor 20 (i.e., the shaft 90 of the compressor8 shown in FIG. 4) is fixed to the shaft hole 27 by shrink fitting,press fitting, or the like.

A plurality of (six in this example) magnet insertion holes 22 in whichthe permanent magnets 25 are inserted are formed along an outerperipheral surface of the rotor core 21. The magnet insertion holes 22are openings. One magnet insertion hole 22 corresponds to one magneticpole. In this example, the rotor 20 is provided with six magnetinsertion holes 22, and thus the rotor 20 has six poles in total. Themagnet insertion hole 22 in this example has a V-shape such that acenter part in the circumferential direction protrudes inward in theradial direction. In this regard, the shape of the magnet insertion hole22 is not limited to the V-shape and may be, for example, a straightshape.

Two permanent magnets 25 are disposed in each magnet insertion hole 22.That is, two permanent magnets 25 are disposed for one magnetic pole. Inthis example, the rotor 20 has six poles as described above, and thustwelve permanent magnets 25 are disposed in total.

The permanent magnet 25 is a flat-plate member elongated in the axialdirection of the rotor core 21, has a width in the circumferentialdirection of the rotor core 21 and has a thickness in the radialdirection of the rotor core 21. The permanent magnet 25 is constitutedby, for example, a rare-earth magnet that contains neodymium (Nd), iron(Fe), and boron (B). The permanent magnet 25 is magnetized in thethickness direction. Two permanent magnets 25 disposed in one magnetinsertion hole 22 are magnetized such that the same magnetic poles areoriented toward the same side in the radial direction.

Flux barriers 26 are formed on both sides of each magnet insertion hole22 in the circumferential direction. The flux barriers 26 are openingsthat are formed continuously with the magnet insertion hole 22. The fluxbarriers 26 are provided for suppressing leakage magnetic flux betweenadjacent magnetic poles (i.e., magnetic flux flowing through inter-poleparts).

In the rotor core 21, a first magnet retention part 23 is formed as aprotrusion at a center part of each magnet insertion hole 22 in thecircumferential direction. Furthermore, in the rotor core 21, secondmagnet retention parts 24 are formed as protrusions on both ends of eachmagnet insertion hole 22 in the circumferential direction. The firstmagnet retention part 23 and the second magnet retention parts 24 areprovided for positioning and retaining the permanent magnets 25 in eachmagnet insertion hole 22.

As described above, the number of slots of the stator 10 (i.e., thenumber of tooth parts 12) is nine, and the number of poles of the rotor20 is six. That is, in the compressor motor 1, a ratio of the number ofpoles of the rotor 20 to the number of slots of the stator 10 is 2:3.

In the compressor motor 1, the connection state of the coils 3 isswitched between the Y connection and the delta connection. When thedelta connection is used, circulating current may flow and may causedegradation of performance of the compressor motor 1. The circulatingcurrent is caused by a third order harmonic wave generated in an inducedvoltage in the winding of each phase. It is known that, in the case of aconcentrated winding where the ratio of the number of poles to thenumber of slots is 2:3, no third order harmonic wave is generated in theinduced voltage and thus degradation of performance of the compressormotor 1 due to the circulating current does not occur if there is noinfluence of magnetic saturation or the like.

(Configuration of Driving Device)

Next, the driving device 100 that drives the compressor motor 1 will bedescribed. FIG. 6 is a block diagram showing a configuration of thedriving device 100. The driving device 100 includes the converter 102that rectifies an output from a power source 101, the inverter 103 thatoutputs an AC voltage to the coils 3 of the compressor motor 1, theconnection switching unit 15 that switches the connection state of thecoils 3, and the controller 50. The converter 102 is supplied withelectric power from the power source 101 which is an AC power source.

The power source 101 is the AC power source of, for example, 200 V(effective voltage). The converter 102 is a rectifier circuit andoutputs a DC voltage of, for example, 280 V. The voltage output from theconverter 102 is referred to as a bus voltage. The inverter 103 issupplied with a bus voltage from the converter 102 and outputs a linevoltage (also referred to as a motor voltage) to the coils 3 of thecompressor motor 1. The inverter 103 is connected to wires 104, 105, and106 which are connected to coils 3U, 3V, and 3W, respectively.

The coil 3U has terminals 31U and 32U. The coil 3V has terminals 31V and32V. The coil 3W has terminals 31W and 32W. The wire 104 is connected tothe terminal 31U of the coil 3U. The wire 105 is connected to theterminal 31V of the coil 3V. The wire 106 is connected to the terminal31W of the coil 3W.

The connection switching unit 15 has switches 15 a, 15 b, and 15 c. Theswitch 15 a connects the terminal 32U of the coil 3U to either the wire105 or a neutral point 33. The switch 15 b connects the terminal 32V ofthe coil 3V to either the wire 106 or the neutral point 33. The switch15 c connects the terminal 32W of the coil 3W to either the wire 104 orthe neutral point 33. In this example, the switches 15 a, 15 b, and 15 cof the connection switching unit 15 are constituted by mechanicalswitches (i.e., relay contacts).

The controller 50 controls the converter 102, the inverter 103, and theconnection switching unit 15. The configuration of the controller 50 isas described with reference to FIG. 3. An operation instruction signalfrom the remote controller 55 received by the signal receiver 56 and anindoor temperature detected by the indoor temperature sensor 54 areinput to the controller 50. Based on the input information, thecontroller 50 outputs a voltage switching signal to the converter 102,outputs an inverter driving signal to the inverter 103, and outputs aconnection switching signal to the connection switching unit 15.

In a state shown in FIG. 6, the switch 15 a connects the terminal 32U ofthe coil 3U to the neutral point 33, the switch 15 b connects theterminal 32V of the coil 3V to the neutral point 33, and the switch 15 cconnects the terminal 32W of the coil 3W to the neutral point 33. Thatis, the terminals 31U, 31V, and 31W of the coils 3U, 3V, and 3W areconnected to the inverter 103, and the terminals 32U, 32V, and 32W areconnected to the neutral point 33.

FIG. 7 is a block diagram showing a state in which the switches 15 a, 15b, and 15 c of the connection switching unit 15 of the driving device100 are switched. In a state shown in FIG. 7, the switch 15 a connectsthe terminal 32U of the coil 3U to the wire 105, the switch 15 bconnects the terminal 32V of the coil 3V to the wire 106, and the switch15 c connects the terminal 32W of the coil 3W to the wire 104.

FIG. 8(A) is a schematic diagram showing the connection state of thecoils 3U, 3V, and 3W when the switches 15 a, 15 b, and 15 c are in thestate shown in FIG. 6. The coils 3U, 3V and 3W are connected to theneutral point 33 at the terminals 32U, 32V and 32W, respectively. Thus,the connection state of the coils 3U, 3V, and 3W is the Y connection(star connection).

FIG. 8(B) is a schematic diagram showing the connection state of thecoils 3U, 3V, and 3W when the switches 15 a, 15 b, and 15 c are in thestate shown in FIG. 7. The terminal 32U of the coil 3U is connected tothe terminal 31V of the coil 3V via the wire 105 (FIG. 7). The terminal32V of the coil 3V is connected to the terminal 31W of the coil 3W viathe wire 106 (FIG. 7). The terminal 32W of the coil 3W is connected tothe terminal 31U of the coil 3U via the wire 104 (FIG. 7). Thus, theconnection state of the coils 3U, 3V, and 3W is the delta connection.

In this way, the connection switching unit 15 is capable of switchingthe connection state of the coils 3U, 3V, and 3W of the compressor motor1 between the Y connection (first connection state) and the deltaconnection (second connection state) by switching the switches 15 a, 15b, and 15 c.

FIG. 9 is a schematic diagram showing coil parts of the coils 3U, 3V,and 3W. As described above, the compressor motor 1 has nine tooth parts12 (FIG. 1), and each of the coils 3U, 3V, and 3W is wound around threetooth parts 12. That is, the coil 3U is obtained by connecting, inseries, U-phase coil parts Ua, Ub, and Uc which are wound around threetooth parts 12. Similarly, the coil 3V is obtained by connecting, inseries, V-phase coil parts Va, Vb, and Vc which are wound around threetooth parts 12. The coil 3W is obtained by connecting, in series,W-phase coil parts Wa, Wb, and We which are wound around three toothparts 12.

(Method for Controlling Operation of Air Conditioner)

FIGS. 10 and 11 are flowcharts showing a method for controlling anoperation of the air conditioner 5. The controller 50 of the airconditioner 5 starts the operation of the air conditioner 5 when thesignal receiver 56 receives a start signal from the remote controller 55(step S101). In this example, the CPU 57 of the controller 50 isactivated.

Then, the controller 50 performs start processing of the air conditioner5 (step S102). Specifically, for example, the rotation of the outdoorfan motor 61 is started.

Then, the controller 50 starts the rotation of the compressor motor 1(step S103). As will be described later, the air conditioner 5 finishesthe previous operation after switching the connection state of the coils3 to the delta connection, and thus the compressor motor 1 is started inthe delta connection. The controller 50 controls the output voltage fromthe inverter 103 to control the rotation speed of the compressor motor1.

Detailed description on controlling the rotation speed of the compressormotor 1 is omitted. For example, the rotation speed of the compressormotor 1 is increased in stages at a predetermined speed in accordancewith the temperature difference ΔT between the indoor temperature Tadetected by the indoor temperature sensor 54 and the set temperature Ts.A maximum allowable rotation speed of the compressor motor 1 is, forexample, 130 rps. Thus, an amount of the refrigerant circulated by thecompressor 8 is increased, so that a cooling capacity is increasedduring a cooling operation, and a heating capacity is increased during aheating operation.

When the indoor temperature Ta approaches the set temperature Ts due toair conditioning effect and the temperature difference ΔT shows atendency to decrease, the controller 50 decreases the rotation speed ofthe compressor motor 1 in accordance with the temperature difference ΔT.When the temperature difference ΔT decreases to a preset temperaturenear zero (but greater than 0), the controller 50 operates thecompressor motor 1 at an allowable minimum rotation speed (for example,20 rps).

When the indoor temperature Ta reaches the set temperature Ts (i.e.,when the temperature difference ΔT is 0 or less), the controller 50stops the rotation of the compressor motor 1 in order to preventovercooling (or overheating). Then, when the temperature difference ΔTbecomes larger than 0 again, the controller 50 restarts the rotation ofthe compressor motor 1. The controller 50 restricts the rotation restartof the compressor motor 1 in a short time period so as not to repeatrotation and stop of the compressor motor 1 in the short time period.Furthermore, when the rotation speed of the compressor motor 1 reaches apreset rotation speed, the inverter 103 starts the field-weakeningcontrol.

After the compressor motor 1 is started, the controller 50 starts therotation of the indoor fan motor 71 (step S104). The indoor fan motor 71rotates at a rotation speed in accordance with the setting set by theremote controller 55, for example. In the air conditioner 5 having anair conditioning capacity of 4 kW within a rated air conditioningcapacity range, the rotation speed of the indoor fan motor 71 is in arange of 0 to 1700 rpm.

The controller 50 determines whether or not an operation stop signal (asignal to stop an operation of the air conditioner 5) is received fromthe remote controller 55 via the signal receiver 56 (step S105). Whenthe operation stop signal is not received, the controller 50 proceeds tostep S106. In contrast, when the operation stop signal is received, thecontroller 50 proceeds to step S109.

In step S106, the controller 50 acquires the temperature difference ΔTbetween the indoor temperature Ta detected by the indoor temperaturesensor 54 and the set temperature Ts. Based on the temperaturedifference ΔT, the controller 50 determines whether or not the switchingfrom the delta connection to the Y connection of the coils 3 isnecessary. That is, the controller 50 determines whether or not theconnection state of the coils 3 is the delta connection and an absolutevalue of the above described temperature difference ΔT is equal to orless than a threshold ΔTr (step S107). The threshold ΔTr is atemperature difference corresponding to an air-conditioning load (alsosimply referred to as a “load”) that is small enough to performswitching to the Y connection.

As described above, ΔT is represented as ΔT=Ts−Ta when the operationmode is the heating operation, and is represented as ΔT=Ta−Ts when theoperation mode is the cooling operation. In this example, the absolutevalue of ΔT and the threshold ΔTr are compared with each other todetermine whether or not the switching to the Y connection is necessary.

When the result of the determination in step S107 indicates that theconnection state of the coils 3 is the delta connection and that theabsolute value of the temperature difference ΔT is equal to or less thanthe threshold ΔTr, the controller 50 outputs a stop signal to theinverter 103 and stops the rotation of the compressor motor 1 (stepS108). After the rotation of the compressor motor 1 is stopped, thecontroller 50 proceeds to step S121 in FIG. 11.

In step S121 in FIG. 11, the controller 50 changes the rotation speed ofthe indoor fan motor 71 to a preset rotation speed N2 and continues therotation of the indoor fan motor 71. Then, the controller 50 outputs aconnection switching signal to the connection switching unit 15 toswitch the connection state of the coils 3 from the delta connection tothe Y connection (step S122).

After the connection state of the coils 3 is switched to the Yconnection, the controller 50 determines whether the compressor motor 1is restartable (i.e., restart of rotation is possible) or not (stepS123). Specifically, for example, a timer is started at the same time aswhen the compressor motor 1 is stopped in step S108, and it isdetermined whether or not a waiting time t1 elapses. The waiting time t1is a time required until a refrigeration pressure in the refrigerationcycle is substantially uniformized, and is, for example, 60 to 300seconds.

Whether the compressor motor 1 is restartable or not can also bedetermined by other methods. For example, it is possible to measure adifferential pressure of the compressor 8, and to determine that thecompressor motor 1 is restartable when the differential pressure fallsbelow a threshold.

When the controller 50 determines that the compressor motor 1 isrestartable (YES in step S123), the controller 50 proceeds to step S118in FIG. 10, and restarts the compressor motor 1. Thus, the rotation ofthe compressor motor 1 is restarted in a state where the connectionstate of the coils 3 is switched to the Y connection.

In contrast, when the result of the comparison in the above describedstep S107 indicates that the connection state of the coils 3 is not thedelta connection (when it is the Y connection), or that the absolutevalue of the temperature difference ΔT is larger than the threshold ΔTr(in other words, when it is not necessary to switch to the Yconnection), the controller 50 proceeds to step S112.

In step S112, it is determined whether or not the switching from the Yconnection to the delta connection is necessary. That is, it isdetermined whether or not the connection state of the coils 3 is the Yconnection and the absolute value of the temperature difference ΔT islarger than the threshold ΔTr.

When the result of the determination in step S112 indicates that theconnection state of the coils 3 is the Y connection and that theabsolute value of the temperature difference ΔT is larger than thethreshold ΔTr (YES in step S112), the controller 50 increases therotation speed of the compressor motor 1 up to a preset rotation speedNmax and continues the rotation of the compressor motor 1 for a presettime period (step S113). This is in order to increase a circulationamount of the refrigerant before the rotation of the compressor motor 1is stopped. The rotation speed Nmax at this time is desirably themaximum value of the rotation speed of the compressor motor 1 within arotation speed range during the normal operation of the compressor motor1. However, the rotation speed at this time is not limited to themaximum value, and it is sufficient to increase the rotation speed ofthe compressor motor 1.

Thereafter, the controller 50 outputs a stop signal to the inverter 103to stop the rotation of the compressor motor 1 (step S114). After therotation of the compressor motor 1 is stopped, the controller 50 changesthe rotation speed of the indoor fan motor 71 to a preset rotation speedN1 and continues the rotation of the indoor fan motor 71 (step S115).Subsequently, the controller 50 outputs a connection switching signal tothe connection switching unit 15 to switch the connection state of thecoils 3 from the Y connection to the delta connection (step S116).

After the connection state of the coils 3 is switched to the deltaconnection, the controller 50 determines whether the compressor motor 1is restartable or not (step S117). The determination of whether thecompressor motor 1 is restartable or not is as described above withregard to step S123. When the controller 50 determines that thecompressor motor 1 is restartable (YES in step S117), the controller 50restarts the compressor motor 1 (step S118). Thus, the rotation of thecompressor motor 1 is restarted in a state where the connection state ofthe coils 3 is switched to the delta connection.

In the case of the delta connection, the compressor motor 1 can bedriven up to a higher rotational speed than in the case of the Yconnection, and thus it is possible to respond to a larger load.Therefore, the temperature difference ΔT between the indoor temperatureand the set temperature can be converged in a short time. Thereafter,the controller 50 returns to the above described step S105.

When the result of the comparison in the above described step S112indicates that the connection state of the coils 3 is not the Yconnection (when it is the delta connection), or that the absolute valueof the temperature difference ΔT is equal to or less than the thresholdΔTr (in other words, when it is not necessary to switch to the deltaconnection), the controller 50 returns to step S105.

Meanwhile, when the operation stop signal is received in step S105described above, the rotation of the compressor motor 1 is stopped (stepS109). Thereafter, the controller 50 switches the connection state ofthe coils 3 from the Y connection to the delta connection (step S110).When the connection state of the coils 3 is already the deltaconnection, this connection state is maintained. Although omitted inFIG. 10, even when the controller 50 receives the operation stop signalduring a period from step S106 to step S117, the controller 50 proceedsto step S109 to stop the rotation of the compressor motor 1.

Then, the controller 50 performs processing to stop the air conditioner5 (step S111). Specifically, the controller 50 stops the indoor fanmotor 71 and the outdoor fan motor 61. Thereafter, the CPU 57 of thecontroller 50 is stopped, and the operation of the air conditioner 5 isterminated.

As described above, when the absolute value of the temperaturedifference ΔT between the indoor temperature Ta and the set temperatureTs is relatively small (that is, when the absolute value is equal to orless than the threshold ΔTr), the compressor motor 1 is operated in theY connection that enables high efficiency operation. When it isnecessary to respond to a larger load, that is, when the absolute valueof the temperature difference ΔT is larger than the threshold ΔTr, thecompressor motor 1 is operated in the delta connection that enablesresponding to the larger load. Thus, operation efficiency of the airconditioner 5 can be enhanced.

(Functions of Air Conditioner)

In the operation of the above described air conditioner 5, the rotationof the compressor motor 1 is stopped before the connection state of thecoils 3 is switched (steps S108 and S114 in FIG. 10), in order toenhance stability of the controlling the compressor motor 1.

Moreover, in order to reduce the load on the compressor motor 1 when thecompressor motor 1 is restarted, a stop period of, for example, 60 to300 seconds (i.e., a time period during which the rotation of thecompressor motor 1 is stopped) is provided before the restart of thecompressor motor 1. This stop period correspond to a time periodrequired until the pressure difference (differential pressure) between adischarge side and a suction side of the compressor 8 sufficientlydecreases, and also corresponds to a time period required until therefrigerant pressure in the refrigeration cycle is substantiallyuniformized.

Meanwhile, when the operation of the air conditioner 5 is stopped, usercomfort is reduced. Specifically, the switching from the Y connection tothe delta connection is performed in a state where the temperaturedifference ΔT between the indoor temperature Ta and the set temperatureTs is large, such as a case where outside air flows into the room byopening and closing of a window. If the operation of the air conditioner5 is stopped in such a state, user comfort is largely reduced.

For this reason, in the first embodiment, the rotation of the indoor fanmotor 71 is continued in the stop period of the compressor motor 1. Evenwhen the rotation of the compressor motor 1 stops, the refrigerantcontinuously flows due to the differential pressure in the compressor 8,and thereby the temperature difference between the refrigerant and theindoor air still remains.

Thus, by rotating the indoor fan motor 71 to cause the indoor fan 7 toblow air, the air subjected to heat exchange with the refrigerant in theindoor heat exchanger 45 can be supplied to the room. That is, in thecooling operation, the air cooled by the heat exchange with therefrigerant in the indoor heat exchanger 45 can be supplied to the room.In the heating operation, the air heated by the heat exchange with therefrigerant in the indoor heat exchanger 45 can be supplied to the room.Thus, reduction in comfort in the room in the stop period of thecompressor motor 1 can be suppressed.

The indoor fan motor 71 starts the rotation before beginning of the stopperiod of the compressor motor 1 (more specifically, step S104 in FIG.10), and continues rotation even after the stop period of the compressormotor 1 begins. Consequently, the number of times of stop and restart ofthe indoor fan motor 71 can be reduced. The motor generally has lowenergy efficiency at the start, and thus the reduction in the number oftimes of stop and restart makes it possible to reduce power consumption.In addition, the number of times that the controller 50 outputs the stopsignal or a restart signal can also be reduced, and thus control of theindoor fan motor 71 can be simplified.

The switching from the delta connection to the Y connection is performedin a state where the indoor temperature approaches the set temperatureand the air conditioning load decreases. Thus, in the stop period of thecompressor motor 1, it is desirable to set the rotation speed N2 of theindoor fan motor 71 to a relatively low speed to thereby reduce powerconsumption. When the indoor temperature is sufficiently close to theset temperature, the rotation of the indoor fan motor 71 may be stopped(as will be described later with reference to FIG. 13).

In contrast, the switching from the Y connection to the delta connectionis performed in a state where the air conditioning load increases, suchas when the indoor temperature approaches the set temperature andthereafter outside air flows into the room by opening and closing thewindow. Thus, it is necessary to increase the rotation speed N1 of theindoor fan motor 71 in the stop period to supplement the airconditioning capacity.

Therefore, the rotation speed N1 of the indoor fan motor 71 at the timeof switching from the Y connection to the delta connection is performedis set higher than the rotation speed N2 of the indoor fan motor 71 atthe time of switching from the delta connection to the Y connection(N1>N2). In the air conditioner 5 of 4 kW within the rated airconditioning capacity range, the rotation speed N1 is, for example, 1700rpm, and the rotation speed N2 is, for example, 1100 rpm.

In the first embodiment, when the switching from the Y connection to thedelta connection is performed, the rotation of the compressor motor 1 isstopped after the compressor motor 1 is rotated at the maximum rotationspeed (Nmax) in a rotation speed range set for the Y connection(hereinafter referred to as a set range) (step S113 described above). Asdescribed above, the heating or cooling capacity (air conditioningcapacity) can be obtained by rotating the indoor fan motor 71 in thestop period of the compressor motor 1, but the air conditioning capacityof the indoor fan motor 71 decreases as the temperature differencebetween the refrigerant and the indoor air decreases.

For this reason, before the rotation of the compressor motor 1 isstopped, the compressor motor 1 is rotated at the maximum rotation speed(Nmax) within the set range for a specified time period to therebyincrease the circulation amount of the refrigerant to increase atemperature difference between the refrigerant and the indoor air inadvance. Consequently, the air conditioning capacity of the indoor fanmotor 71 in the stop period of the compressor motor 1 can be enhanced.

Although the compressor motor 1 rotates at the maximum rotation speedwithin the set range in this example, the rotation speed of thecompressor motor 1 is not limited to the maximum rotation speed. It issufficient that the rotation speed of the compressor motor 1 is higherthan, for example, the rotation speed of the compressor motor 1 when thedetermination in step S112 is performed.

Although the rotation speeds of the indoor fan motor 71 are set to N1and N2 in this example (steps S115 and S121), the rotation speed of theindoor fan motor 71 may be increased in accordance with a decrease inthe difference between the temperature of the refrigerant and thetemperature of the air. Furthermore, although the indoor fan motor 71 isconstantly rotated during the stop period of the compressor motor 1 inthis example, the indoor fan motor 71 may be rotated only for a timeperiod within the stop period of the compressor motor 1 (for example,only when a certain condition is satisfied as will be described in thesecond embodiment and the like).

In the above described operation of the air conditioner 5, thedetermination of necessity of the switching from the delta connection tothe Y connection (step S107) and the determination of necessity of theswitching from the Y connection to the delta connection (step S112) aresuccessively performed. However, the switching from the delta connectionto the Y connection is performed in a case where the air conditioningload decreases (the indoor temperature approaches the set temperature),and there is a low possibility that a sudden increase in the airconditioning load occurs thereafter, and thus the frequent switching ofthe connection is less likely to occur.

At the end of the operation of the air conditioner 5, the connectionstate of the coils 3 is switched to the delta connection (step S110),and thus, at the start of the operation of the air conditioner 5, thecompressor motor 1 is started in the delta connection (step S103). Atthe start of the operation of the air conditioner 5, the differencebetween the indoor temperature and the set temperature is generallylarge (in other words, the air conditioning load is large). For thisreason, by starting the compressor motor 1 in a state where theconnection state of the coils 3 is in the delta connection, thedifference ΔT between the indoor temperature Ta and the set temperatureTs can be converged in a shorter time.

(Effects of First Embodiment)

As described above, in the air conditioner 5 of the first embodiment,the stop period during which the rotation of the compressor motor 1 isstopped is provided before the connection switching unit 15 switches theconnection state of the coils 3, and the indoor fan motor 71 is rotatedfor at least a time period within the stop period. Thus, the airconditioning capacity can be supplemented by air blowing by the indoorfan 7, and the reduction in user comfort can be suppressed.

When the connection switching unit 15 switches the connection state ofthe coils 3 from the Y connection (first connection state) to the deltaconnection (second connection state), the compressor motor 1 is drivenat the increased rotation speed before the stop period of the compressormotor 1 begins, and thus the circulation amount of the refrigerant canbe temporarily increased to increase the temperature difference betweenthe refrigerant and the indoor air. Consequently, the air conditioningcapacity achieved by air blowing by the indoor fan 7 in the stop periodcan be enhanced.

The indoor fan motor 71 starts the rotation before the stop period ofthe compressor motor 1 begins, and the indoor fan motor 71 continuesrotation in the stop period, and thus the number of times of stop andstart of the indoor fan motor 71 can be reduced and the powerconsumption can be reduced.

The rotation speed N1 of the indoor fan motor 71 in the stop period ofthe compressor motor 1 when the connection state of the coils 3 isswitched from the Y connection to the delta connection, and the rotationspeed N2 of the indoor fan motor 71 in the stop period of the compressormotor 1 when the connection state of the coils 3 is switched from thedelta connection to the Y connection satisfy N1>N2. Therefore, theindoor fan 7 can perform the air blowing operation depending onmagnitude of the air conditioning load.

Since the connection state of the coils 3 is switched based on theindoor temperature detected by the indoor temperature sensor 54, theoperation state of the compressor 8 can be quickly adapted to a suddenchange in the air conditioning load, and thus comfort can be increased.

Since the connection state of the coils 3 is switched between the Yconnection (first connection state) and the delta connection (secondconnection state) in which a line voltage is lower than in the Yconnection, the connection state suitable for the rotation speed of thecompressor motor 1 can be selected.

Modifications

FIG. 12 is a block diagram showing another configuration example of thedriving device 100 in the first embodiment. While the connectionswitching unit 15 (FIG. 6) of the driving device 100 described aboveincludes the mechanical switches 15 a, 15 b, and 15 c, a connectionswitching unit 16 in the configuration example shown in FIG. 12 includessemiconductor switches 16 a, 16 b, and 16 c.

The semiconductor switches 16 a, 16 b, and 16 c are constituted by, forexample, MOS transistors or the like. The semiconductor switch 16 aconnects the terminal 32U of the coil 3U to either the wire 105 or theneutral point 33. The semiconductor switch 16 b connects the terminal32V of the coil 3V to either the wire 106 or the neutral point 33. Thesemiconductor switch 16 c connects the terminal 32W of the coil 3W toeither the wire 104 or the neutral point 33.

In this configuration example, the connection switching unit 16 includesthe semiconductor switches 16 a, 16 b, and 16 c, and thus the connectionstate of the coils 3 can be switched at high speed, and powerconsumption can be reduced. Other components are as described withreference to FIG. 6.

Second Embodiment

Next, a second embodiment of the present invention will be described.FIG. 13 is a flowchart showing an operation in the second embodiment.Processing shown in FIG. 13 is performed following step S108 in FIG. 10,as is the case with the processing shown in FIG. 11.

In the above described first embodiment, when the switching from thedelta connection to the Y connection is performed, the controller 50stops the rotation of the compressor motor 1 (step S108 in FIG. 10) andthen rotates the indoor fan motor 71 at the rotation speed N2 (step S121in FIG. 11).

In contrast, in the second embodiment, when the switching from the deltaconnection to the Y connection is performed, the controller 50 stops therotation of the compressor motor 1, and then the controller 50 comparesa threshold Tb and an absolute value of a temperature difference ΔTbetween the indoor temperature Ta detected by the indoor temperaturesensor 54 and the set temperature Ts (i.e., the temperature differenceΔT acquired in step S106 of FIG. 10) (step S131). When the absolutevalue of the temperature difference ΔT is equal to or less than thethreshold Tb, the controller 50 stops the rotation of the indoor fanmotor 71 (step S135).

In contrast, when the absolute value of the temperature difference ΔT islarger than the threshold Tb, the indoor fan motor 71 is rotated at therotation speed N2 as in the first embodiment (step S132). The thresholdTb is a value smaller than the above described threshold Tr, and is atemperature difference that is so small that it is not necessary torotate the indoor fan motor 71 in the stop period of the compressormotor 1.

Thereafter, the controller 50 switches the connection state of the coils3 from the delta connection to the Y connection (step S133), waits untilthe compressor motor 1 becomes restartable (step S134), and thenrestarts the compressor motor 1 (step S118 in FIG. 10). The order ofsteps S133 and S134 may be reversed. The switching from the Y connectionto the delta connection is performed in the same manner as in the firstembodiment.

The switching from the delta connection to the Y connection is performedin a state where the indoor temperature Ta approaches the settemperature Ts and the air conditioning load decreases. Thus, in a casewhere the indoor temperature Ta is sufficiently close to the settemperature Ts, the reduction in comfort in the room is small even whenthe indoor fan 7 does not blow air. In the second embodiment, when theabsolute value of the temperature difference ΔT between the indoortemperature Ta and the set temperature Ts is equal to or less than thethreshold Tb (i.e., when the indoor temperature Ta is sufficiently closeto the set temperature Ts), the rotation of the indoor fan motor 71 isstopped in the stop period of the compressor motor 1, and thus powerconsumption can be reduced.

As described above, in the second embodiment, when the indoortemperature Ta detected by the indoor temperature sensor 54 is differentfrom the set temperature Ts, the indoor fan motor 71 is rotated in thestop period of the compressor motor 1. More specifically, when theabsolute value of the difference ΔT between the indoor temperature Tadetected by the indoor temperature sensor 54 and the set temperature Tsis larger than the threshold Tb, the indoor fan motor 71 is rotated inthe stop period of the compressor motor 1. In contrast, when thedifference ΔT is equal to or less than the threshold Tb, the rotation ofthe indoor fan motor 71 is stopped in the stop period of the compressormotor 1. Thus, when the indoor temperature Ta is sufficiently close tothe set temperature Ts, the rotation of the indoor fan motor 71 isstopped in the stop period of the compressor motor 1, and thereforepower consumption can be reduced.

Third Embodiment

Next, a third embodiment of the present invention will be described.FIG. 14 is a flowchart showing an operation in the third embodiment.Processing shown in FIG. 14 is performed following step S108 in FIG. 10,as is the case with the processing shown in FIGS. 11 and 13.

In the above described second embodiment, when the switching from thedelta connection to the Y connection is performed, the threshold Tb iscompared with the absolute value of the temperature difference ΔTbetween the indoor temperature Ta detected by the indoor temperaturesensor 54 and the set temperature Ts, and the rotation of the indoor fanmotor 71 is stopped when the absolute value of the temperaturedifference ΔT is equal to or less than the threshold Tb (steps S131 andS135 in FIG. 13). As the temperature difference ΔT, the temperaturedifference ΔT acquired in step S106 of FIG. 10 is employed.

In contrast, in the third embodiment, the controller 50 continuouslyacquires the temperature difference ΔT between the indoor temperature Tadetected by the indoor temperature sensor 54 and the set temperature Tsduring the stop period of the compressor motor 1 (step S145). Further,the controller 50 compares the temperature difference ΔT with thethreshold Tb (step S141). When the absolute value of the temperaturedifference ΔT is equal to or less than the threshold Tb, the controller50 stops the rotation of the indoor fan motor 71 (step S144). When theabsolute value of the temperature difference ΔT is larger than thethreshold Tb, the controller 50 rotates the indoor fan motor 71 at therotation speed N2 (step S142).

Thereafter, the controller 50 waits until the compressor motor 1 becomesrestartable (step S143). Then, the controller 50 switches the connectionstate of the coils 3 from the delta connection to the Y connection (stepS146), and restarts the compressor motor 1 (step S118 in FIG. 10).

The stop period of the compressor motor 1 continues for 60 to 300minutes, for example, and the indoor temperature may change in the stopperiod due to the air blowing by the indoor fan 7. In the thirdembodiment, the indoor temperature Ta is continuously detected by theindoor temperature sensor 54 during the stop period. When the indoortemperature Ta is sufficiently close to the set temperature Ts, therotation of the indoor fan motor 71 is stopped, but otherwise the indoorfan motor 71 is rotated. Thus, the air blowing operation by the indoorfan 7 can be performed in accordance with change in the indoortemperature in the stop period of the compressor motor 1, and thereforecomfort can be increased.

As described above, in the third embodiment, the temperature differenceΔT between the indoor temperature Ta and the set temperature Ts iscontinuously acquired during the stop period of the compressor motor 1.When the absolute value of the temperature difference ΔT is equal to orless than the threshold Tb, the rotation of the indoor fan motor 71 isstopped, whereas when the absolute value of the temperature differenceΔT is larger than the threshold Tb, the indoor fan motor 71 is rotated.Thus, the air blowing operation of the indoor fan 7 can be performed inaccordance with change in the indoor temperature during the stop periodof the compressor motor 1. Therefore, comfort can be increased.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described.FIG. 15 is a flowchart showing a method for controlling an operation ofan air conditioner in the fourth embodiment. In the flowchart of FIG.15, steps S151 and step S152 are added between step S115 and step S116of the flowchart in FIG. 10.

The switching from the Y connection to the delta connection is performedin a state where the air conditioning load increases, such as whenoutside air flows into the room by opening and closing the window afterthe indoor temperature Ta approaches the set temperature Ts. However,since the indoor fan 7 blows air in the stop period of the compressormotor 1, the indoor temperature Ta approaches the set temperature Ts andthe air conditioning load decreases, and thus the switching to the deltaconnection may become unnecessary.

Thus, in the fourth embodiment, in the stop period of the compressormotor 1, the indoor fan motor 71 is rotated, and a temperaturedifference change rate Tv is determined. The temperature differencechange rate Tv is a change rate (change rate relative to time) of theabsolute value of the difference between the indoor temperature Ta andthe set temperature Ts. When the temperature difference change rate Tvis smaller than a specified value (threshold) Tc, the switching to thedelta connection is not performed. The temperature difference changerate Tv is defined by the following equation (1). The specified value Tcis a negative value.

$\begin{matrix}{{Tv} = {\frac{d}{dt}{{{Ts} - {Ta}}}}} & (1)\end{matrix}$

Specifically, when the switching from the Y connection to the deltaconnection is performed, the controller 50 stops the rotation of thecompressor motor 1 (step S114) and rotates the indoor fan motor 71 atthe rotation speed N1 (step S115). Then, the controller 50 acquires thetemperature difference change rate Tv (the above described equation (1))which is the change rate of the absolute value of the difference betweenthe indoor temperature Ta detected by the indoor temperature sensor 54and the set temperature Ts (step S151).

Then, the controller 50 compares the temperature difference change rateTv acquired in step S151 with the specified value Tc previously set(step S152). The specified value Tc (<0) is a change rate of thetemperature difference (absolute value) when the temperature differencedecreases at a pace such that switching to the delta connection is notnecessary. The specified value Tc is determined by experiments or thelike, and is preset. It is also possible to set different specifiedvalues Tc for the heating operation and the cooling operation.

When the temperature difference change rate Tv is equal to or largerthan the specified value Tc in step S152, the switching to the deltaconnection is performed (step S116), waiting is performed until thecompressor motor 1 becomes restartable (step S117), and then thecompressor motor 1 is restarted (step S118).

In contrast, when the temperature difference change rate Tv is smallerthan the specified value Tc in step S152, the controller 50 proceeds tostep S117 without performing switching to the delta connection (stepS116), waits until the compressor motor 1 becomes restartable, and thenthe compressor motor 1 is restarted (step S118).

Thus, during the stop period of the compressor motor 1, the connectionof the coils is not switched from the Y connection to the deltaconnection, when the change rate Tv of the absolute value of thedifference between the indoor temperature Ta and the set temperature Tsis smaller than the specified value Tc (<0) due to the air blowing bythe indoor fan 7 (that is, when the difference between the indoortemperature Ta and the set temperature Ts rapidly decreases). That is,frequent switching of the connection state of the coils 3 can besuppressed, and thus power consumption can be reduced. Steps other thansteps S151 and S152 are the same as those in the method for controllingthe operation (FIGS. 10 and 11) of the first embodiment.

As described above, in the fourth embodiment, the temperature differencechange rate Tv is acquired during the stop period of the compressormotor 1, and whether or not the connection of the coils is to beswitched is determined based on the acquired temperature differencechange rate Tv. Thus, frequent switching of the connection state of thecoils 3 can be suppressed, and power consumption can be reduced.

The second embodiment (FIG. 13) or third embodiment (FIG. 14) may becombined with the fourth embodiment.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described. Inthe first embodiment described above, the connection state of the coils3 is switched between the Y connection and the delta connection.However, the connection state of the coils 3 may be switched between aseries connection and a parallel connection.

FIGS. 16(A) and 16(B) are schematic diagrams for explaining theswitching of the connection state of the coils 3 in the fifthembodiment. As shown in FIG. 16(A), three-phase coils 3U, 3V, and 3W areconnected in the Y connection. The coil parts Ua, Ub, and Uc of the coil3U are connected in series, the coil parts Va, Vb, and Vc of the coil 3Vare connected in series, and the coil parts Wa, Wb, and Wc of the coil3W are connected in series. That is, the coil parts of each phase of thecoils 3 are connected in series.

In contrast, as shown in FIG. 16(B), while three-phase coils 3U, 3V, and3W are connected in the Y connection, the coil parts Ua, Ub, and Uc ofthe coil 3U are connected in parallel, the coil parts Va, Vb, and Vc ofthe coil 3V are connected in parallel, and the coil parts Wa, Wb, and Wcof the coil 3W are connected in parallel. That is, the coil parts ofeach phase of the coils 3 are connected in parallel. Switching of theconnection state of the coils 3 shown in FIGS. 16(A) and 16(B) can beachieved, for example, by providing each of the coil parts of the coils3U, 3V, and 3W with a selector switch.

When n is defined as the number of the coil parts (i.e., the number ofcolumns) connected in parallel in each phase, the line voltage decreasesby a factor of 1/n by switching from the series connection (FIG. 16(A))to the parallel connection (FIG. 16(B)). That is, the motor efficiencycan be enhanced by switching the connection state of the coils 3 betweentwo connection states where line voltages are different.

FIGS. 17(A) and 17(B) are schematic diagrams for explaining anotherconfiguration example of the fifth embodiment. As shown in FIG. 17(A),three-phase coils 3U, 3V, and 3W are connected in the delta connection.The coil parts Ua, Ub, and Uc of the coil 3U are connected in series,the coil parts Va, Vb, and Vc of the coil 3V are connected in series,and the coil parts Wa, Wb, and Wc of the coil 3W are connected inseries. That is, the coil parts of each phase of the coils 3 areconnected in series.

As shown in FIG. 17(B), while three-phase coils 3U, 3V, and 3W areconnected in the delta connection, the coil parts Ua, Ub, and Uc of thecoil 3U are connected in parallel, the coil parts Va, Vb, and Vc of thecoil 3V are connected in parallel, and the coil parts Wa, Wb, and We ofthe coil 3W are connected in parallel. That is, the coil parts of eachphase of the coils 3 are connected in parallel. Also in this case, themotor efficiency can be enhanced by switching the connection state ofthe coils 3 between two connection states where line voltages aredifferent.

As described above, in the fifth embodiment, the motor efficiency can beenhanced by switching the connection state of the coils 3 between theseries connection and the parallel connection.

At least one of the second embodiment (FIG. 13), the third embodiment(FIG. 14), or the fourth embodiment (FIG. 15) may be combined with thefifth embodiment.

Although in the above described first to fifth embodiments, theconnection state of the coils 3 is switched based on the temperaturedifference ΔT between the indoor temperature Ta detected by the indoortemperature sensor 54 and the threshold Tr, the connection state of thecoils 3 may be switched based on, for example, the rotation speed of thecompressor motor 1. The rotation speed of the compressor motor 1 can bedetected using a current sensor or the like attached to the compressormotor 1. In this regard, since the rotation speed of the compressormotor 1 may vary, the rotation speed of the compressor motor 1 iscompared with the reference value, and it is determined whether or notthe rotation speed continuously exceeds a reference value for a certaintime period.

Although the rotary compressor has been described as an example of thecompressor 8 in the above described first to fifth embodiments, themotor of each of the embodiments may be applied to a compressor otherthan the rotary compressor.

Although the desired embodiments of the present invention have beenspecifically described, the present invention is not limited to theabove described embodiments, and various changes or modifications can bemade to the above described embodiments without departing from the scopeand spirit of the present invention.

What is claimed is:
 1. An air conditioner comprising: a compressorhaving a compressor motor including coils; an indoor fan having a fanmotor; a switch connected to the coils, the switch switching aconnection state of the coils between a first connection state and asecond connection state in which a line voltage is lower than a linevoltage in the first connection state; and a controller to control thecompressor motor, the fan motor, and the switch, the controllerproviding a stop period during which rotation of the compressor motorstops before the switch switches the connection state of the coils,wherein the controller causes the fan motor to rotate at a rotationspeed N1 in the stop period before the switch switches the connectionstate from the first connection state to the second connection state,wherein the controller causes the fan motor to rotate at a rotationspeed N2 in the stop period before the switch switches the connectionstate from the second connection state to the first connection state,the rotation speed N1 and the rotation speed N2 satisfying N1>N2, andwherein, when the switch switches the connection state of the coils fromthe first connection state to the second connection state, thecontroller increases a rotation speed of the compressor motor beforestopping the rotation of the compressor motor.
 2. The air conditioneraccording to claim 1, wherein the controller rotates the fan motorbefore the stop period begins, and the controller causes the fan motorto continue rotation in the stop period.
 3. The air conditioneraccording to claim 1, further comprising: a temperature sensor to detectan indoor temperature, wherein the controller performs controls thecompressor motor and the switch based on the indoor temperature and aset temperature.
 4. The air conditioner according to claim 3, whereinthe controller rotates the fan motor in the stop period when the indoortemperature is different from the set temperature.
 5. The airconditioner according to claim 3, wherein the controller rotates the fanmotor in the stop period when an absolute value of a difference betweenthe indoor temperature and the set temperature is larger than athreshold.
 6. The air conditioner according to claim 3, wherein thecontroller stops rotation of the fan motor in the stop period when anabsolute value of a difference between the indoor temperature and theset temperature is equal to or less than a threshold, and wherein thecontroller rotates the fan motor in the stop period when an absolutevalue of the difference between the indoor temperature and the settemperature is larger than the threshold.
 7. The air conditioneraccording to claim 3, wherein the controller does not switch theconnection of the coils from the first connection state to the secondconnection state in the stop period when a change rate of an absolutevalue of a difference between the indoor temperature and the settemperature is smaller than a prescribed value.
 8. The air conditioneraccording to claim 3, wherein the controller switches the connectionstate of the coils based on the indoor temperature.
 9. The airconditioner according to claim 1, wherein the coils are three-phasecoils, and wherein the first connection state is a state in which thethree-phase coils are connected in Y connection, and the secondconnection state is a state in which the three-phase coils are connectedin delta connection.
 10. The air conditioner according to claim 1,wherein the coils are three-phase coils that are connected in Yconnection or delta connection, wherein the first connection state is astate in which coil parts of each of the three-phase coils are connectedin series, and wherein the second connection state is a state in whichcoil parts of each of the three-phase coils are connected in parallel.11. The air conditioner according to claim 1, wherein the switch is amechanical switch or a semiconductor switch.
 12. The air conditioneraccording to claim 1, wherein, when the connection state of the coils isswitched from the second connection state to the first connection state,the rotation speed of the compressor motor is not increased beforestopping the rotation of the compressor motor.
 13. A method forcontrolling an operation of an air conditioner, the air conditionercomprising a compressor having a compressor motor including coils and anindoor fan having a fan motor, the method using a switch connected tothe coils and a controller to control the compressor motor, the fanmotor, and the switch, the method comprising: switching a connectionstate of the coils using the switch between a first connection state anda second connection state in which a line voltage is lower than a linevoltage in the first connection state, wherein a stop period duringwhich rotation of the compressor motor stops is provided before the stepof switching the connection state, and the fan motor is rotated for atleast a time period within the stop period, wherein the fan motor isrotated at a rotation speed N1 in the stop period before the connectionstate is switched from the first connection state to the secondconnection state, wherein the fan motor is rotated at a rotation speedN2 in the stop period before the connection state is switched from thesecond connection state to the first connection state, the rotationspeed N1 and the rotation speed N2 satisfying N1>N2, and wherein, whenthe connection state of the coils is switched from the first connectionstate to the second connection state in the switching step, a rotationspeed of the compressor motor is increased before stopping the rotationof the compressor motor.